1. Field of the Invention
The present invention relates generally to a system and method for managing mobility based on MIPv6 (Mobile Internet Protocol Version 6), and in particular, to a system and method for supporting regional mobility using access routers each having an anchor point function.
2. Description of the Related Art
Internet users desire to use a high-quality Internet service anytime and anyplace, and with the performance improvement of mobile terminals such as portable computers and PDAs (Personal Digital Assistants) and the development of wireless communication technology, the number of users has remarkably increased.
An IP (Internet Protocol) address in an Internet addressing system is comprised of a network identifier field and a host identifier field. The network identifier field is a part for identifying a network, while the host identifier field is a part for identifying a host within the network. If a mobile terminal moves to another network, the network identifier is changed and accordingly, an IP address of the mobile terminal is also changed. In an IP layer, since packets are routed according to a network identifier of a destination address, the mobile terminal cannot receive packets when it moves to another network. If a mobile terminal desires to continue communication even in another network, the mobile terminal should change its IP address so that it has a network identifier of the network each time it moves to another network. In this case, upper layer connection such as TCP (Transmission Control Protocol) connection is not guaranteed. Therefore, a protocol called “Mobile IP” capable of guaranteeing mobility is used to enable communication while maintaining an existing address intact.
If the number of wireless Internet users is increased, as is the current tendency, the increasing IP address demands cannot be satisfied with the existing IPv4 (Internet Protocol version 4) address system. Therefore, active searches have been carried out on a method for supporting mobility using a MIPv6 protocol that has recently attracted public attention as a future Internet protocol.
A fundamental operation of the MIPv6 will be described. If a mobile node (MN) moves from a home network to an external network, the mobile node acquires a care-of address (CoA) from an agent of a subnet where it is currently located. Also, when a mobile node moves from an external one subnet to a new subnet, the mobile node acquires a new CoA from the new subnet. The mobile node binds the CoA with a home address and registers the binding result in corresponding nodes (CNs) with which a home agent of the home network and the mobile node itself communicate. Thereafter, the corresponding nodes set a destination of a packet which is to be transmitted to the mobile node at the CoA, and transmit the packet to the mobile node. The home agent of the home network intercepts the packet being transmitted to the mobile node using the original home address as a destination address, and tunnels the intercepted packet to the mobile node.
If the mobile node is geographically or topologically remote from the home agent or the corresponding nodes, a time required for binding update is increased. During the binding update time, packets to be transmitted to the mobile node may be lost in an access router. A concept called “localized mobility management (LMM)” has been introduced as a scheme for solving this problem. LMM refers to a method in which even though a mobile node moves to a new subnet, a packet can be routed to the mobile node without affecting the binding registered in a home agent or the corresponding nodes. In this method, a mobile node can move to a new subnet while maintaining an IP address of the mobile node, as seen by the home agent of the mobile node and by the corresponding nodes.
Hierachical MIPv6 (HMIPv6) has been proposed as a conventional technique that satisfies the LMM condition. In HMIPv6, a new node called a “mobile anchor point (MAP)” is defined. The MAP is a router located in a domain visited by a mobile node, and can also be located in any layer among routers in a hierachical structure.
The MAP has a function of intercepting all packets to be delivered to a mobile node registered therein and directly tunneling the intercepted packets to a current CoA, or on-line CoA (LCoA), of the mobile node. The mobile node, when it moves to a new MAP domain, binding-registers a region or a regional CoA (RCoA), acquired from the new MAP, and its home address in the corresponding nodes or in the home agent. However, when the mobile node moves within the MAP domain, the mobile node binding-updates the RCoA and the LCoA only in the MAP without binding-updating them in the corresponding nodes or in the home agent.
A boundary of the MAP domain is defined by access routers that advertise MAP information to connected mobile nodes. FIG. 1 illustrates an example of a conventional network topology with one MAP domain. Referring to FIG. 1, MAP 101 is connected to a plurality of access routers (ARs) 103, and each access router 103 is connected again to one or multiple access routers (ARs) 105. The access routers 105 advertise information on the MAP 101 to connected mobile nodes through a MAP optima message. With introduction of the MAP concept, a waiting time caused by handoff between two access routers is minimized. In addition, the MAP reduces signals that must be transmitted and received to/from the exterior of a regional domain in MIPv6, and smoothly performs handoff of a mobile node.
As described above, the MAP can be located in any layer among routers in a hierachical structure or access routers. However, once a position of the MAP is determined, only the access routers located in a lower layer of the MAP can use the MAP as anchor point. That is, the HMIPv6 can be undesirably realized only in a fixed hierachical network topology. Accordingly, there is a demand for a method capable of satisfying the LMM condition without restriction of the network topology like in the conventional HMIPv6.
In addition, in the hierachical network topology, when a mobile node is connected to an access router of a lower layer in a MAP domain, a length of a tunnel through which a packet transmitted to the access node is tunneled can become excessively long. An increase in tunnel length means that encapsulation and decapsulation of a packet transmitted to the mobile node must be repeated several times, causing an increase in a transmission time of a packet and a load of the routers that perform tunneling. Thus, there is a demand for an LMM realization method capable of restricting an excessive increase in tunnel length.
The HMIPv6 is divided into a basic mode and an extended mode according to a method in which a mobile node acquires RCoA. In the basic mode, RCoA is formed from (1) a subnet prefix of MAP broadcasted in a MAP option and (2) an interface identifier of a mobile node. In the extended mode, a mobile node receives RCoA assigned to any one of the interfaces of a MAP through a MAP option and uses the received RCoA intact. In either mode, the mobile node must acquire both LCoA and RCoA. Particularly, in order for the mobile node to acquire RCoA, a MAP option must be advertised from each router. Therefore, an RCoA acquisition procedure becomes a primary factor of increasing overhead in network operation. Thus, it is necessary to reduce the overhead caused by the RCoA acquisition procedure.